Stretch wrapping is a packaging technique which dispenses a sheet of stretch wrap packaging material in a stretched condition around a load, to cover and retain the load in a packaged condition. Current stretch wrapping apparatus utilize film dispensers having two closely spaced rollers to stretch a web of thermoplastic stretch film packaging material. These rollers are known as prestretch rollers, with a downstream roller having a faster surface speedy than an upstream roller. This differential in surface speeds between the downstream and upstream rollers stretches the packaging material between the prestretch rollers in the dispensing direction.
Typically, the prestretch rollers were equal in diameter, and powered, such that the downstream prestretch roller had a faster surface speed than the upstream prestretched roller, to thereby stretch the web of stretch film over its yield point in the dispensing direction.
Preferably, the upstream and downstream prestretched roller should be closely spaced together during operation to prevent "neck down" (lost of film width) of the film web as it is being stretched in the dispensing direction.
Another desirably feature is to reduce or eliminate theoretical elongation of the stretch film. This is achieved by increasing the amount of surface contact of the stretch film with the prestretch rollers. The conventional path of stretch film around the prestretch rollers affords approximately one quarter of the circumference of the roller in contact with the stretch film.
Finally, it is desirable to achieve are liable elongation of the stretch film, which allows slight film imperfections to base through the system without causing a film failure.